1608 SPRING HILL ROAD, SUITE 400 • VIENNA, VIRGINIA • 22182 • 703.893.6600 • FAX 703.821.8236 

MEMO 

TO: Fernald Work Group 

FROM: Joyce Lipsztein, SC&A 

DATE: January 30, 2012 

SUBJECT: SC&A Final Position on the Th-232 In-vivo Data Quality and Adequacy for 

FEMP Workers 

 

INTRODUCTION 

This memo presents SC&A’s final position and conclusions regarding the quality and adequacy 

of Th-232 in-vivo data for use in reconstructing internal doses to workers at Fernald. 

Specifically, this memo focuses on the period of 1968–1978, when thorium lung burdens were 

reported in units of mg of Th. 

A considerable amount of material and reports have been exchanged between NIOSH and SC&A 

on the usability of chest count data to reconstruct Th-232 internal exposures for monitored and 

unmonitored workers starting in 1968. The original coworker model was delivered in 2008 

titled: Thorium In Vivo Coworker Study for FEMP – A Proposed Attachment for ORAUT-TKBS0017-5, Rev. 1, 2008 (ORAUT 2008). In response, SC&A prepared a white paper review of the 

NIOSH coworker study in June of 2010 (SC&A 2010). Subsequent to this initial review, there 

have been several work group discussions and exchanges of information in the form of additional 

white papers and informal responses. The timeline of discussions and additional responses is 

summarized as follows: 

 February 2, 2011: NIOSH releases its initial response to SC&A’s review in two 

documents; FMPC In Vivo Chest Count Bias Adjustment (NIOSH 2011a) and Response 

to SCA comments on Fernald Th232 coworker study (NIOSH 2011b). 

 February 8, 2011: SC&A review and NIOSH responses first discussed at the work group 

meeting. 

 April 19, 2011: Issues are further discussed at the work group meeting. This work group 

meeting was the first instance in which the chest count data were discussed in detail. 

 May 23, 2011: NIOSH releases report entitled, FMPC – Mobile In Vivo Radiation 

Monitoring Laboratory Calibration and Data Interpretation – Draft 01 (NIOSH 2011c). 

 August 3, 2011: SC&A releases second white paper, SC&A Response to NIOSH White 

Paper on FMPC Mobile In Vivo Radiation Monitoring Laboratory Calibration and Data 

Interpretation and Associated References (SC&A 2011), in response to previously 

released NIOSH documents. 

 August 8, 2011: Recent exchange of white papers and documented responses are 

discussed at work group meeting 
Memo to the Fernald Work Group 2 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

 2011d. 

 

 November 10, 2011: NIOSH releases white paper response titled, NIOSH Response to 

SC&A Response to NIOSH White Paper on FMPC MIVRML Calibration, Rev. 00. 

(NIOSH 2011d). 

The exchange of information that NIOSH provided in 2011 has been especially informative 

regarding the new documentation uncovered for the MIVRML, which was not available at the 

time of SC&A’s initial review (SC&A 2010). NIOSH has presented a thorough and intense 

review of documentation related to the potential use of Th-232 chest count data. SC&A has 

performed a detailed examination of all the documents provided by NIOSH and has concluded 

that monitoring results provided in milligrams of thorium cannot be quantified with sufficient 

accuracy in terms of real exposures to be used to bound thorium lung burdens, body burdens, or 

doses in an Special Exposure Cohort (SEC) context for the period of 1968–1978.1

 The 

following Sections (1–4) detail SC&A’s findings related to the adequacy of the thorium in-vivo 

monitoring for reconstructing internal doses. Section 1 describes the inherent uncertainty in 

measuring thorium using chest counting techniques. Section 2 discusses the proposed use of

statistical models to demonstrate the adequacy of the thorium data as presented in NIOSH

Section 3 discusses some observed inconsistencies in the worker records that illustrate the 

uncertainties associated with in-vivo monitoring for thorium. Section 4 presents some additional 

issues related to the uncertainty of thorium measurements that were discussed in NIOSH 2011d. 

1.0 SC&A FINDINGS ON THE SIGNIFICANCE AND UNCERTAINTY INVOLVING 

THORIUM IN-VIVO RESULTS 

1.1 FINDING 1.1 

SC&A has been unable to locate any documentation demonstrating how the results given in mg 

of thorium were derived for the time period of 1968–1978. Documentation made available by 

NIOSH did not refer to the methods used specifically for in-vivo monitoring of FMPC workers. 

Because Th-232 could not have been measured directly, measurements were done using one or 

more of the gamma-emitting daughter products. However, it is not clear which daughter 

radionuclide(s) was used to derive the stated results in mg of thorium. Actinium-228 (Ac-228), 

Pb-212, Tl-208, or some combination of these daughter products could have been used to 

estimate the lung burden of thorium. NIOSH 2011b assumes that measurements of the Th-232 

daughter product Pb-212 were used to develop the lung burdens of thorium, yet provides no 

supporting documentation to verify this key assumption. 

One possibility is that the gamma emissions from both Ac-228 and Pb-212 were used to develop 

the values in milligrams of thorium. One indication of this possibility is the fact that these 

isotopes were measured and reported in the period after 1978, instead of the previously reported 

“mg of Th.” This may be further evidenced by a handwritten document from 1976 titled, Lung 

Counter Thorium Calibration Runs, March 26, 1976 (Author Unknown 1976). This document 

describes a case in which the ratio of Pb-212/Ac-228 activities was used to derive the age of the 

1

 1968–1978 encompasses the monitoring period when lung burdens were reported in the units of mg 

thorium. 
Memo to the Fernald Work Group 3 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

thorium source after purification, and to derive the conversion of the measured Ac-228 activity 

to a thorium activity and associated mass (mg). 

This handwritten document also demonstrates the large uncertainties in derived thorium lung 

burdens that rely on equilibrium ratio estimates, which are, in turn, based on Ac-228 and Pb-212 

measurements. The in-vivo results for Pb-212 in this particular case were 2.85 nCi and 3.15 nCi, 

with an average of 3.0 nCi. The results for Ac-228 were 2.75 nCi and 2.8 nCi, with an average 

of 2.78 nCi. The ratio of the average results (Pb-212/Ac-228) was equal to 1.08, which indicates 

that the age of the source was approximately 4.3 years after purification, and that the associated 

thorium burden was 56 mg. The document further states that if the ratio (Pb-212/Ac-228) was 

assumed to be equal to 1, the calculated thorium burden would decrease to 27.6 mg. Due to the 

large uncertainties in lung burden estimates that result from small measurement variability, the 

paper suggests that the assignment of lung burdens should be based on previous knowledge 

of source separation times, which could likely be obtained from the health physics 

department. 

In SC&A’s view, many relevant questions remain that have not been sufficiently answered, such 

as: 

 Were the burdens derived in the 1968–1978 period based on the ratio of Pb-212/Ac-228 

or only one daughter product? 

 Were they based on knowledge of the age of the source? To what degree were the 

assignments of body burdens dependent on the person in charge of the measurements? 

 Were the assumptions potentially different before and after 1976 (when the handwritten 

document discussed above was produced)? 

It is worthwhile to mention that there are no results equal to 27.6 mg or 56 mg of thorium in any 

thorium results currently available to NIOSH and SC&A, so it is unclear whether this type of 

analysis represents a Fernald worker. 

1.2 FINDING 1.2 

NIOSH 2011d, Section 3.1, states that most of the monitoring data represent “analytical 

background,” and that this indicates that these records represent normal thorium lung burdens for 

a population of unexposed workers. It appears that NIOSH is positing that because the results 

are by and large below the minimum detectable activity (MDA) for the MIVRML counting 

system, it can be inferred that the workers were unexposed and that their intakes are 

characterized by a null distribution. Such an inference holds true only if the counting system is 

sufficiently sensitive to accurately measure intakes that result in meaningful doses. 

To demonstrate the dosimetric significance of chest burdens at or near the stated MDA of 6 mg 

thorium, SC&A quantified organ doses that could have been accrued under four different 

exposure scenarios. For a 6mg Th-232 chest burden result taken at face value (without 

contesting its significance), SC&A has estimated the corresponding committed equivalent dose 

to bone surface and to the lungs for various exposures scenarios for Type M intakes of the 
Memo to the Fernald Work Group 4 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

radionuclide. It is further assumed that the thorium exposure was only due to exposures of 

Th-232 and Th-228, without the intake of the progeny. Except for freshly purified sources, the 

calculated doses are underestimations, as the doses due to simultaneous intake of the daughters 

are not taken into account. The scenarios are based on possible exposure times and possible invivo chest monitoring intervals after exposures for workers at FMPC. 

Scenario 1: Worker exposed during 30 days to thorium Type M compounds (worked with 

thorium during 30 days): 

1.a Worker monitored 60 days after first day of exposure (30 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 1.3 Sv 

 Lung Committed Equivalent Dose: 0.1 Sv 

1.b Worker monitored 90 days after first day of exposure (60 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 1.7 Sv 

 Lung Committed Equivalent Dose: 0.15 Sv 

1.c Worker monitored 180 days after first day of exposure (150 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 3.2 Sv 

 Lung Committed Equivalent Dose: 0.3 Sv 

1.d Worker monitored 270 days after first day of exposure (240 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 5.6 Sv 

 Lung Committed Equivalent Dose: 0.5 Sv 

1.e Worker monitored 1 year after first day of exposure (235 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 9.7 Sv 

Lung Committed Equivalent Dose: 0.8 Sv 

Scenario 2: Worker Exposed during 90 days to thorium Type M compounds: 

2.a Worker monitored 180 days after first day of exposure (90 days after last day of 

exposure) 

Bone Surface Committed equivalent dose: 2.6 Sv 

 Lung Committed Equivalent Dose: 0.24 Sv 

2.b Worker monitored 270 days after first day of exposure (180 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 4.6 Sv 

 Lung Committed Equivalent Dose: 0.4 Sv 
Memo to the Fernald Work Group 5 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

2.c Worker monitored 1 year after first day of exposure (275 days after last exposure 

day) 

Bone Surface Committed Equivalent Dose: 8 Sv 

Lung Committed Equivalent Dose: 0.7 Sv 

Scenario 3: Worker Exposed during 180 days to thorium Type M compounds: 

 3.a Worker monitored 270 days after first day of exposure (90 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 3.3 Sv 

Lung Committed Equivalent Dose: 0.3 Sv 

3.b Worker monitored 1 year after first day of exposure (185 days after last day of 

exposure): 

Bone Surface Committed Equivalent dose: 6 Sv 

Lung Committed Equivalent Dose: 0.5 Sv 

 Scenario 4: Worker Exposed during 365 days to thorium Type M compounds: 

Worker monitored 1 day after last day of exposure: 

Bone Surface Committed Equivalent dose: 2.6 Sv 

Lung Committed Equivalent Dose: 0.2 Sv 

SC&A has demonstrated in these examples that intakes at or near 6 mg can result in very high 

[Sv-level (100 rem)] organ doses. Clearly then, the workers had significant exposure potential, 

but the MIVRML counting system was not adequately sensitive to quantify those intakes. 

The 11 graphs presented by NIOSH (NIOSH 2011d) representing thorium chest counts of 

Fernald workers show that most of the results were positive, but well below the stated MDA. 

Depending on the exposure time of the workers and the interval between exposure and 

monitoring, positive but unquantified results might be associated with very high doses. For 

example, for Scenarios 3.b and 1.d, a 1-mg chest burden result might be associated with about 

1-Sv bone surface equivalent dose. For Scenarios 1.e and 2.c, a 1-mg chest burden will be 

associated with a bone surface equivalent dose higher than 1 Sv. 

In summary, SC&A finds NIOSH’s contention that the thorium results that were below the 6 mg 

detection limits indicate that workers were “clean” and only exposed to normal background 

exposures to be highly questionable. 

1.3 FINDING 1.3 

It is not clear to SC&A how results below the 6 mg MDA were calculated. Thorium burdens 

presented in units of mg had to be calculated through the measurements of the daughters. If the 

ratio of activities of Pb-212/Ac-228 was used to calculate the age of the thorium source, it would 

not be possible to correctly calculate the age using Pb-212 and Ac-228 results that essentially 

represent electronic background noise. 
Memo to the Fernald Work Group 6 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

The document Counter Thorium Calibration Runs, March 26, 1976 (Author Unknown 1976) is 

the only document that exemplifies the use of daughter’s activities to calculate thorium lung 

burdens. The activity/mass of thorium was assigned using Ac-228 measurement. When Ac-228 

is used, an underestimation of the thorium burden by a factor of more than 100 can occur. 

The underestimation of thorium activity by the measurement of Ac-228 activities is illustrated in 

Figure 3 of NIOSH 2011c, as a function of time after purification of the source. This 

underestimation was also discussed in SC&A 2010, which states: 

For example, the activity ratio Ac-228:Th-232 in the lungs would be only about 

0.06 at 6 months after inhalation of initially pure thorium, and about 0.11 at 

1 year, assuming no migration of in-growing Ac-228 from Th-232. 

Further complicating the issue are uncertainties related to the biokinetics of the thorium progeny 

in the lung, as explained in Finding 1.4. 

1.4 FINDING 1.4 

There are many difficulties associated with the measurement of thorium daughter nuclides. One 

of the main problems is the equilibrium ratio in the lung. The quantity of daughter radionuclides 

retained in the lung from a Th-232 intake depends in part on the equilibrium conditions of the 

original outside source. In addition, the daughters’ physico-chemical behavior does not follow 

the parent nuclide. Even in its most soluble form, there is generally a long-term retention of 

thorium in the lungs following its intake. In contrast, thorium daughter products, such as radium 

and lead, are more readily absorbed from the respiratory tract into systemic circulation. This is 

true for the daughters that are inhaled together with the original thorium, and also for the 

daughters that are formed within the lung. Even for the slow dissolving components of Type S 

material, decay products formed by alpha emission that escape the particulate substrate will 

behave like a more soluble form in the lung (Type M, for example). Thus, the daughter nuclides, 

whether formed within the lung or inhaled with the original source, will leave the lung at a 

higher rate than the thorium itself, and thorium lung burdens based on gamma emissions from 

those daughter products retained in the lung will be underestimated. 

In addition, the solubility of the daughters formed within the lung might be different from the 

daughters that were inhaled. Also, it is likely the residence time in the lung of Ac-228 and of 

Pb-212 may be different. The translocation of thorium daughters in the lung was discussed in 

detail in SC&A 2011. 

1.5 FINDING 1.5 

The problem of translocation, as discussed in Finding 1.3, was already known at the time of the 

in-vivo measurements and is explained in the paper by West (1965). The West paper, which was 

discussed in SC&A 2011, describes the problem of the different rates of translocation of 

daughters from the lung in the following manner: 

A third factor complicating the interpretation of personnel monitoring results is 

the probability of the metabolic or physical translocations of daughters away 
Memo to the Fernald Work Group 7 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

from the location of the parent stored in the body. Such translocation can affect 

the reliability and sensitivity of the in vivo interpretation if the gammas measured 

are those from daughters subject to translocation. On the other hand, 

translocation could be used in dose estimates if the amount of translocated 

daughters eliminated from the body can be related to the amount of parent 

remaining. (West 1965) 

NIOSH 2011d attempts to disqualify the importance of this problem by citing the following from 

the West document: “in vivo measurements are ‘primarily qualitative’ but can be ‘made 

quantitative by establishing or estimating thorium to daughter ratios” (West 1965). NIOSH 

further states that they have evaluated and quantified these limitations, and that bounding, 

claimant-favorable ratios and correction factors for use in a thorium coworker model were 

provided. SC&A does not agree with this position. SC&A firmly believes that for the period in 

which measurement results were given in mg of thorium (1968–1978), it is not possible to infer 

the raw measurements of the daughter nuclide(s) that are required in order to compute the 

thorium lung burden. In fact, it is currently unknown if one or more daughters were actually 

measured. Thus, any assumptions that are based on unknown raw measurements cannot be 

reasonably established. 

It is noteworthy that for the 1979–1988 period, when activity results of Ac-228 and Pb-212 are 

available, SC&A believes that it might be possible to assign bounding claimant-favorable 

conditions to calculate the lung burdens. However, SC&A has not yet seen any such calculations 

or assumptions; the assumptions to date have been related to the age of the external source. 

1.6 FINDING 1.6 

A careful examination of the available in-vivo files for Fernald workers shows that thorium 

burdens were not used to quantitatively relate the measured burdens to limits for restriction of 

exposure. Instead, monitoring records appear to indicate that the objective was to obtain 

uranium lung burdens in order to calculate the percentage of the maximum permissible lung 

burden (MPLB) they represented. There were no similar calculations identified for thorium. 

SC&A has examined a list of in-vivo thorium results above 6 mg of thorium (the assumed 

MDA), which amount to a total of 75 results from 59 workers. About 70% of the measurements 

did not have a follow-up sample taken within a 6-month period. For the workers that were 

monitored more than once within a 6-month period, there was no apparent relation between the 

value of the first result and the increased frequency of monitoring. 

SC&A has also examined the hardcopy NOCTS files of 15 claimants identified from the list of 

59 workers that had results above 6 mg of thorium. None of the worker files contained any 

attempt to calculate the % of MPLB for thorium. Conversely, almost all the workers had 

calculations of the % of MPLB for uranium. Furthermore, almost all of the in-vivo monitoring 

results that were repeated within a period of 6 months were geared to the calculation of % of the 

uranium MPLB. 
Memo to the Fernald Work Group 8 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

SC&A concludes that the results of thorium in-vivo monitoring from these files were not used to 

calculate the workers’ exposures or an associated percentage of the applicable restriction limits 

for thorium at the time. Based on the currently available records, the results appear to have only 

been used qualitatively, as indicated in West (1965). 

2.0 DISCUSSION OF THE USE OF STATISTICAL MODELS TO ESTABLISH THE 

ADEQUACY OF IN-VIVO DATA PROVIDED IN MILLIGRAMS OF THORIUM 

In the first few pages of NIOSH 2011d, NIOSH presents several graphs of standard normal 

quantiles versus thorium chest burdens in milligrams (mg) for thorium results for the years 

1968–1978. The graphs show that the sub-MDL results appear to be normally distributed, which 

one would expect, with a small number of values that fall above the normal probability line and 

that may represent real (though qualitative) thorium intakes. NIOSH draws the following 

conclusion from these graphical representations: 

The significant feature of these plots is the large number of persons (2617) 

counted over these time periods which were measured below the MDA. Most of 

these counts are analytical background and this indicates that these were workers 

that were “clean” and represent normal thorium burdens that are in workers that 

were not exposed. 

As noted above in Finding 1.2, SC&A believes this statement to be misleading. In reality, the 

preponderance of sub-MDA values reflects an insufficiently sensitive measurement system, 

because intakes at values below 6 mg can nonetheless result in Sv-level organ doses. In addition, 

the normal thorium lung content in non-exposed populations is around 3 μg (Iyengar et al. 2004, 

Ibrahim et al. 1983), 3 orders of magnitude lower than the mg amount, reported for FMPC 

workers. 

SC&A also notes that the graphs are based on mg thorium results without the benefit of 

substantiating Ac-228 and Pb-212 measurements, as discussed in detail in the preceding 

paragraphs. That is, the results are taken at face value and are presumed to be sufficiently 

accurate representations of worker intakes. SC&A reiterates that the graphs are based on values 

that cannot be reconstituted in terms of the raw data that was used at the time workers were 

monitored. That is, the statistical analysis was performed on values that cannot be related to 

actual exposures/intakes. As stated previously in Finding 1.6, SC&A believes that the thorium 

in-vivo results reported in mg were intended to be qualitative in nature, and were not meant to 

quantitatively represent thorium exposures. The corollary is that conclusions regarding accrued 

exposures and doses cannot be drawn from the mg thorium results, because there is currently no 

supporting data upon which to base these conclusions. 
Memo to the Fernald Work Group 9 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

3.0 INCONSISTENCIES IDENTIFIED IN INDIVIDUAL WORKER FILES WHICH 

DEMONSTRATE THE UNCERTAINTY IN MEASUREMENTS GIVEN IN 

MILLIGRAMS OF THORIUM 

3.1 FINDING 3.1 

For many workers that were measured more than one time within a 6-month period, the values 

obtained are not consistent with the expected residence time in the lung, as explained in 

Section 2.3 of SC&A 2010. NIOSH’s response to this finding was that there are high 

imprecisions from the measurements below the limits of detection (NIOSH 2011c). NIOSH used 

an example given by SC&A, in which a measurement result of 10.2 mg is followed by one taken 

after 41 days with a result of 0.2 mg. NIOSH stated that 40 days after monitoring, a result below 

the 6-mg detection limit is expected for Type M thorium compounds. Notwithstanding the large 

imprecisions in measurements below the MDA, SC&A does not agree with this last assertion on 

the basis of known biokinetic processes. 

Assuming the thorium solubility was Type M, the minimum expected result 41 days after the 

10.2 mg measurement would be 6.00 mg, which is at the presumed MDA. This expected result 

is much different from the 0.2 mg listed in the in-vivo records. In addition, the 6.0 mg value was 

calculated by assuming that the 10.2 mg result was obtained 1 day after the potential exposure. 

If, in reality, the monitoring took place at a later time after exposure, the expected thorium lung 

burden would be higher than 6.0 mg. 

SC&A would like to reinforce this point with data taken from another worker who was 

monitored on March 22, 1976, and had a 25 mg thorium lung burden result. This worker was 

monitored again on July 12, 1976, with a thorium result of 0.03 mg. With the given time 

interval, the maximum expected decrease for Type M material would be about 32%. This would 

lead to a result of approximately 8 mg and not the stated value of 0.03 mg. This is an example 

where both the first measurement result and the expected one are higher than the 6 mg “detection 

limit.” 

3.2 FINDING 3.2 

SC&A 2010, Section 2.2, contains 22 entries that were identified as reporting both Th (mg) and 

Pb-212 (nCi) results, which allows for the direct comparison of the two values. These entries 

were shown in Table 1 of SC&A 2010. The values of Th (mg) and the raw results for Pb-212 

were recreated below as Table 1, adding Ac-228 raw results, dates, and locations of workers. 

The three highest thorium results and two other positive thorium results had corresponding 

negative Pb-212 measurements. This casts serious doubt on the assumption that Pb-212 results 

were used to calculate the thorium values in mg. 

Three positive thorium results were taken in the period 1968–1978. One of the results, 4.3 mg of 

thorium, was reported on April 26, 1971. The corresponding Pb-212 result was negative 

(-0.04nCi), but the Ac-228 activity was reported as positive (0.05 nCi), although probably below 

the MDA. A result equal to 2.2 mg Th-232 was reported in April 13, 1977, which had 

corresponding negative results for Pb and Ac-228 (-0.1 nCi for both). 
Memo to the Fernald Work Group 10 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

On the other hand, there were 9 positive results equal to 2.1 mg of thorium reported in June and 

October 1979 that had corresponding Ac-228 and Pb-212 positive results. Lead-212 (Pb-212) 

activity results ranged from 0.19 to 0.40 nCi, while Ac-228 results ranged from 0.33 to 0.7 nCi. 

Only one Pb-212 result was below the 1987 MDAs of 0.23 nCi for Pb-212 and 0.24 nCi for 

Ac-228, as reported in NIOSH 2011c. The 9 reported lung burdens of 2.1 mg of thorium are 

below the assumed MDA of 6 mg. Based on those 9 results, dates, and workers’ locations, 

there is no apparent relation of the thorium mass results with Ac-228 or Pb-212 activities. 

Another positive thorium result, listed as 0.3 mg reported on April 6, 1977, does not provide any 

information on how the actual thorium results were calculated. The corresponding values were 

0.15 nCi for Pb-212 and 0.06 nCi for Ac-228. The highest value in Table 1 is 5.10 mg of 

thorium, reported on June 4, 1980. The corresponding Pb-212 result was negative (-0.04) and 

the Ac-228 result was 0.01 nCi. 

The contemporaneous results of Ac-228, Pb-212, and Th-232 shown in Table 1 demonstrated 

how difficult it is to try to reconstruct the workers’ exposures based solely on thorium results 

given in mg. They further show that the quantitative significance of the thorium results in mg is 

indeterminable. 

Table 1: Comparison of Contemporaneously Reported Thorium Mass (mg), 

Pb-212 and Ac-228 Activities (nCi) 

Reported Thorium 

Result (mg) 

Reported Pb-212 

Activity (nCi) 

Reported Ac-228 

Activity (nCi) Monitoring Date Location or Plant # 

-5.00 -0.04 -0.02 8/29/1974 7 or Pilot 

-0.60 -0.08 0.03 06/08/88 Maintenance 

-0.54 -0.18 -0.01 06/12/86 5 

-0.16 -0.16 -0.09 06/23/87 5 

-0.12 0.06 0.01 07/10/73 6 

-0.05 -0.05 0.02 05/02/87 Maintenance 

-0.01 -0.01 0.05 12/09/86 No Information 

0.01 -0.06 -0.08 05/02/77 Mech 

0.30 0.15 0.06 04/06/77 6 

1.81 -0.10 0.04 08/09/85 5 

2.10 0.25 0.35 06/02/79 7 or Pilot 

2.10 0.30 0.5 06/09/79 7 or Pilot 

2.10 0.40 0.7 06/12/79 7 or Pilot 

2.10 0.40 0.65 06/19/79 7 or Pilot 

2.10 0.40 0.5 10/08/79 4 

2.10 0.19 0.33 10/22/79 4 

2.10 0.27 0.33 10/29/79 4 

2.10 0.28 0.41 10/17/79 4 

2.10 0.29 0.39 10/15/79 4 

2.20 -0.10 -0.1 04/13/77 Mech 

4.30 -0.04 0.05 04/26/71 Inspection 

5.10 -0.04 0.01 06/04/80 Mech 
Memo to the Fernald Work Group 11 SC&A – January 30, 2012 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

4.0 ADDITIONAL UNCERTAINTIES DISCUSSED IN NOVEMBER 2011 NIOSH’S 

WHITE PAPER 

4.1 FINDING 4.1 

The issue of calibration phantoms was discussed in Section 3.2 of SC&A 2011, with a 

subsequent response from NIOSH provided in NIOSH 2011d, page 15. SC&A agrees that it is 

possible to assign a suitable geometric standard deviation that would cover uncertainties derived 

from the system calibration using the REMAB phantom. The REMAB phantom was used from 

the early 1970s to 1983. However, no information was provided to address the uncertainties 

related to the phantom used in the period prior to this, 1968–1970. 

4.2 FINDING 4.2 

The issue of the assumed equilibrium ratio of 0.42 Th-232/Th-228 was discussed in Section 3.6 

of SC&A 2011, with a subsequent response provided in NIOSH 2011d, page 17. SC&A agrees 

with the response provided by NIOSH; however, the problem remains that in the period from 

1968–1978, only results in mg of thorium are provided, with no associated Pb-212 component. 

As detailed in the previous sections, those results cannot be reconstructed, and it is not known if 

Pb-212 was used to calculate Th-232 exposures. If Ac-228 was used without Pb-212, the 

thorium lung burden could be underestimated by a factor of 100 or more. In addition, the 

biokinetics of the daughters are different from the parent, which most likely translates into 

further underestimation of the thorium lung burden and of the exposures. 

CONCLUSION 

SC&A believes that coworker models can only yield meaningful results when they are based on 

quantities that have some inherent meaning in terms of intakes experienced by workers. The 

existing documentation on the mg thorium data is inconsistent and does not clarify how the 

thorium values were calculated from the measured daughter products. The values in mg of 

thorium might have been underestimated by a factor of 100 or more. In summary, SC&A 

believes that the thorium lung burdens reported in units of mg from 1968–1978 cannot be 

reconstructed or associated with meaningful intakes and are, therefore, not sufficiently accurate 

to be used by NIOSH to derive thorium intake rates. 
Memo to the Fernald Work Group 12 SC&A – January 30, 2012 

 This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 

NOTICE:

REFERENCES 

Author Unknown 1976. Lung Counter Thorium Calibration Runs, March 26, 1976. March 26, 

1976 Document Capture No. Y/AB-NIOSH-2007-067. SRDB Ref ID 32612. 

Ibrahim, S.A., M.E. Wrenn, N.P. Singh, N. Cohen, and G. Saccomano. Thorium concentration 

in human tissues from two U.S. populations. Health Physics 44:213–220. 

Iyengar, G.V., H. Kawamura, H.S. Dang, R.M. Parr, J.W. Wang, S.Y. Cho, and 

E.S. Natera, 2004. Contents of Cesium, Iodine, Strontium, Thorium, and Uranium in Selected 

Human Organs of Adult Asian Population, Health Physics 87: 151-159. 

NIOSH 2011a. FMPC In Vivo Chest Count Data Bias Adjustment. National Institute for 

Occupational Safety and Health, Cincinnati, Ohio. January 19, 2011. Transmitted February 3, 

2011. 

NIOSH 2011b. Response to SCA comments on Fernald Th232 coworker study. National 

Institute for Occupational Safety and Health, Cincinnati, Ohio. Transmitted February 3, 2011. 

NIOSH 2011c. Morris, R., FMPC – Mobile In Vivo Radiation Monitoring Laboratory 

Calibration and Data Interpretation – Draft 01. National Institute for Occupational Safety and 

Health, Cincinnati, Ohio. May 6, 2011. Transmitted May 23, 2011. 

NIOSH 2011d. Morris, R., Smith, B., Labone, T., Response to SC&A Response to NIOSH White 

Paper on FMPC MIVRML Calibration. National Institute for Occupational Safety and Health, 

Cincinnati, Ohio. November 8, 2011. Transmitted November 10, 2011. 

ORAUT 2008. Thorium In Vivo Coworker Study for FEMP – A Proposed Attachment for 

ORAUT-TKBS-0017-5, Revision 1. Oak Ridge Associated Universities Team, Cincinnati, Ohio. 

January 8, 2008. 

SC&A 2010. Review of “Thorium In-Vivo Coworker Study for FEMP – A Proposed Attachment 

for ORAUT-TKBS-0017-5, Rev. 1.” SC&A, Vienna, Virginia, and Saliant, Inc., Jefferson, 

Maryland. June 2010. 

SC&A 2011. Lipsztein, J., SC&A Response to NIOSH White Paper on FMPC Mobile In Vivo 

Radiation Monitoring Laboratory Calibration and Data Interpretation and Associated 

References. SC&A, Inc., Vienna, Virginia, and Saliant, Inc., Jefferson, Maryland. August 3, 

2011. Transmitted August 3, 2011. 

West, C.M., 1965. Health Physics Considerations Associated with Thorium Processing, Report 

Number Y-KB-53, Union Carbide Corporation, Nuclear Division, Oak Ridge, Tennessee, Y-12 

Plant, 1965.